This proposal is to study the efficaciousness of a large stroke volume (100 ml) small elliptical heart orothotopically placed in 50 kg animals. This work includes hemodynamics, blood-material interaction, pathophysiology, durability, and reliability, and post mortem evaluation. These studies will be conducted by implanting this innovative device into a series of calves (short-term studies) and adult, nonrowing sheep (long-term studies). The hemodynamics will be monitored in the short-term experiments utilizing open-port catheters and both series will be studied with the nonnivasive cardiac output and diagnostic monitor during rest and exercise. Standard blood chemistries and cellular levels will be routinely monitored. Organ function will also be evaluated. At the termination of the experiments, detailed autopsies will be conducted on both the animals and the devices. The derived data will be analyzed and compared with data obtained from previous JARVIK-7 heart implant studies. Placement of a 100 cc stroke volume elliptical TAH in 50 kg recipients without compromising other organ function makes possible the application of this blood pump to a large segment of the human population with end-stage heart failure, who possess thoracic dimensions too small to accommodate the JARVIK-7 total artificial heart. Fabrication is made easier and more reliable by the simple design of the ventricular housing and allows the future application of injection molding to the manufacture of this blood pump. This two-year project will provide the data regarding pumping capabilities, regulation, blood compatibility, and durability, which is necessary for perfecting and characterizing this new total artificial heart. Long-term use of this more efficient design will verify its superior utilization of the available thoracic space when the natural heart is excised without harming surrounding structures. This new elliptical total artificial heart opens up new areas of research and clinical application of mechanical replacement of the natural heart.